![]() Meiotic recombination is not only necessary to create new allele combinations that generate genetic diversity, but is also essential in ensuring accurate chromosome segregation at the first meiotic division because the crossover acts as a tether between homologues, which ensures that each homologue will properly align at the metaphase plate and thereby correctly attach to the spindle. Meiotic crossing over involves the generation of meiotic double-strand breaks (DSBs), which are subsequently repaired either as crossovers or non-crossovers ( Fig. Once homologues have aligned, synapsis can proceed with the formation of the synaptonemal complex (SC), a protein structure that supports and maintains homologues in close juxtaposition and serves as a scaffold for crossover-promoting recombination factors. A key step in meiosis I is the recognition of homologous chromosomes, which then align and pair along the length of the chromosome. During this process, a single round of replication is followed by two rounds of chromosome segregation: in the first division (meiosis I), homologous chromosomes segregate, whereas in the second division, sister chromatids segregate (meiosis II). Meiosis is the specialised reductive division that generates haploid cells. ![]() This Commentary aims to highlight recent advances in our understanding of the factors that promote or prevent meiotic crossing over. A discussion of crossover interference, assurance and homeostasis, which influence crossing over on a chromosome-wide and genome-wide scale – in addition to current models for the generation of interference – is also included. In this review, we focus on the factors that influence DSB positioning, the proteins required for the formation of recombination intermediates and how the processing of these structures generates either a crossover or non-crossover in various organisms. Nevertheless, several recent papers have revealed important insights into the factors that control the decision between crossover and non-crossover formation in meiosis, including DNA elements that determine the positioning of meiotic DSBs, and the generation and processing of recombination intermediates. ![]() What determines where meiotic DSBs are created and whether a crossover or non-crossover will be formed at any particular DSB remains largely unclear. During meiosis, excess meiotic double-strand breaks (DSBs) are generated a subset of these breaks are repaired to form crossovers, whereas the remainder are repaired as non-crossovers. Meiotic crossovers are essential for ensuring correct chromosome segregation as well as for creating new combinations of alleles for natural selection to take place.
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